test against Django 2.2 (#51516)

setup.py

@@ -107,7 +107,7 @@ setup(
         'Programming Language :: Python :: 2',
     ],
     install_requires=[
-        'django>=1.10,<2',
+        'django<2.3',
         'isodate',
         'psycopg2',
         'jsonschema',

tox.ini

@@ -5,7 +5,7 @@
 
 [tox]
 toxworkdir = {env:TMPDIR:/tmp}/tox-{env:USER}/zoo/{env:BRANCH_NAME:}
-envlist = py3-coverage
+envlist = py3-{dj111,dj22}-coverage
 
 [testenv]
 # django.contrib.auth is not tested it does not work with our templates
@@ -21,6 +21,8 @@ usedevelop =
   coverage: True
   nocoverage: False
 deps = 
+  dj111: django<2
+  dj22: django<2.3
   pip>8
   pytest-flakes
   pg: psycopg2